1. Technical Field
The present invention relates to the electrolytic treatment of an acid solution, for instance the recovery of metals from an acid solution. One example of the present invention is the preparation of a more concentrated solution containing hexavalent chromium from a dilute electroplating rinse solution containing hexavalent chromium.
2. Description of the Prior Art
In the electroplating of a workpiece in a chromic acid solution, the electroplating cell is generally followed by one or more rinse tanks in which the plated workpiece is rinsed. It is desirable to maintain a low concentration of chromium ions in the rinse water. Accordingly, where more than one rinse tank is used, fresh water can be introduced into the last rinse tank, and cascaded from the last rinse tank to the penultimate rinse tank, on up to the rinse tank closest to the electroplating cell. The rinse tank closest to the electroplating cell experiences a build-up of chromium ions in the tank. The rinse solution in this rinse tank has too high a concentration of chromium ions for sewer disposal of the solution In addition, it is economically desirable to recover the chromium ions if possible.
U.S. Pat. No. 4,302,304 discloses a process for treating a chromic acid-containing metal plating waste water. The metal plating waste water is fed to the cathode chamber of an electrolytic cell. The cell is partitioned with a diaphragm. A DC voltage is applied between the cell anode and the cathode. This causes the migration of chromate or dichromate ions to the anode chamber. Chromic acid is recovered in the anode chamber of the cell, and reusable water is recovered in the cathode chamber of the cell. The diaphragm may be made of glass fiber, porcelain, cloth, or of porous high molecular weight polymers. The chromic acid withdrawn from the anode chamber is sufficiently concentrated that it can also be reused.